1. The Field of the Invention
This invention relates to a novel acid-labile polymer and a resist composition containing the same, and more particularly to a novel polymer useful for preparation of photoresist for fine works using various radiations, for examples, a charged particle rays such as electron beam (e-beam), X-rays such as synchrotron radiation and far infrared radiation such as KrF excimer laser or ArF excimer laser.
2. Related Prior Art
Recently, with an increase in the large-scale integration (LSI) of semiconductor devices, there is a demand for super-fine patterns of which the size is 0.13 xcexcm or smaller in manufacturing very large scale integration (VLSI). Accordingly, the radiations utilized as a conventional exposure source, such as g- or i-ray, have become replaced with those that have a shorter wavelength, and lithographic techniques using far ultraviolet rays (e.g., KrF or ArF excimer laser), X-ray or electron beam have lately attracted considerable attention. Especially, an ArF excimer laser is a most promising exposure source in the future lithography requiring a pattern size of 0.13 xcexcm or smaller.
A resist composition suitable for fine works using such radiations is composed of a component having an acid-liable functional group (hereinafter referred to as xe2x80x9cpolymerxe2x80x9d), a component generating an acid upon light radiation (hereinafter referred to as xe2x80x9cphotoacid generatorxe2x80x9d), and a solvent. Such a resist composition may additionally comprise a dissolution inhibitor or a base additive.
On the other hand, the polymer used as a principal component of the resist composition should have a low absorbance in the wavelength range of the exposure source.
The chemically amplified resist used in the conventional radiation of a KrF excimer laser is usually composed of a phenol-based polymer as a principal component, with a disadvantage in that the polymer shows a high absorbance in the range of the ArF excimer laser region due to aromatic rings included therein. Such a high absorbance in the wavelength range may deteriorate the perpendicularity and, hence, the resolution of the resulting photoresist pattern.
In order to solve the aforementioned problem, many studies have been made on resins destitute of unsaturated hydrocarbon or aromatic group as a polymer suitable for use in a photoresist composition sensitive to an ArF excimer laser. Examples of such polymers that exhibit a relatively low absorbance in the wavelength range of the ArF excimer laser may include acrylate polymer, olefin polymer and maleic anhydride-cycloolefin polymer.
Such polymers as disclosed in the prior documents include an acrylate polymer containing an alicyclic group (See. SPIE (1996, 2724, 334)) and a maleic anhydride-cycloolefin polymer (See. SPIE (1996, 2724, 355)). The acrylate polymer had a low optical absorbance in the wavelength range of the ArF excimer laser but shows a poor etching resistance. The maleic anhydride-cycloolefin polymer is superior in etching resistance to the acrylate polymer but has a high optical absorbance in the wavelength range of the ArF excimer laser, resulting in poor perpendicularity of the photoresist pattern. Furthermore, the maleic anhydride monomer is liable to hydrolysis, and formulation of a resist composition comprising the maleic anhydride monomer has low storage stability.
In order to overcome the problem as such, many studies have been conducted to minimize variations in property through hydrolysis of anhydride group in the storage, that is, by minimizing the content of a maleic anhydride monomer or by not adding a maleic anhydride monomer. As a result, it generated an alicylic group in the polymer main chain having a high etching resistance and maleic derivatives or fumaric derivatives similar to an acrylate monomer, which generated in the polymer main chain, thereby making an increase in etching resistance by protecting of main chain when it was dry-etched.
It is therefore an object of the present invention to provide a polymer that can be used to prepare a resist pattern having high sensitivity, resolution, developability, dry-etching resistance, transparency at the excimer laser wavelength, good adhesion and low dependency upon the substrate.
It is another object of the present invention to provide a chemically amplified resist composition having the above-mentioned polymer to be induced by far infrared beam such as a KrF excimer laser or a ArF excimer laser.
In order to achieve the aforementioned objects of the present invention, there is provided a multi-cyclic polymer represented by the following formula 1.
At this time, R1, R2 and R6 are independent of one another and include a hydrogen atom or an alkyl, alkoxymethylene, alkoxyethylene, phenyl, alkoxyalkylene, alkylphenyl, alkoxyphenyl, allyl, benzyl, alkylbenzyl, alkoxybenzyl containing 1 to 34 carbon atoms with or without an hydroxy, ether, ester, carbonyl, acetal, epoxy, nitrile or aldehyde; R5 is a hydrogen atom, an alkyl or alkoxy group containing 1 to 18 carbon atoms; R7 is a hydrogen atom, an alkyl group containing 1 to 18 carbon atoms, an alkyl group containing alkoxy 1 to 18 carbon atoms or an alkyl group containing ester of 1 to 18 carbon atoms; R3 and R4 are independent and include a hydrogen atom, hydroxy, nitrile, aldehyde, hydroxymethylene, and alkylcarbonyloxy, alkyl, hydroxyalkylene, alkoxycarbonyl, alkoxymethylene or alkoxyalkanyl group containing 1 to 18 carbon atoms; X is olefin derivatives, vinyl ether derivatives or styrene derivatives containing 1 to 40 carbon atoms, alternatively these derivatives may include hydroxy, ester, alkoxyalkyloxycarbonyl, ketone or ether; a, b, c, d, e and f are a number representing a repeating unit in the main chain, wherein, if a+b+c+d+e+f=1, the content of a and b is 0 to 0.7, respectively, and, if (a+b)/(a+b+c+d+e+f) greater than 0.3, the content of c, d, e and f is 0 to 0.9, respectively (where, n is an integer of 0 or 1).
Furthermore, a resist composition of the present invention consists of multi-cyclic polymer, as represented by the above formula 1, containing acid generating agent, additive and solvent.
Now, the present invention will be described in further detail as set forth hereunder.
The former acrylate polymer has a low glass transition temperature (Tg) and low etching resistance, so that it has not been utilized in the field of semiconductor device process. Maleic anhydride cycloolefin polymer has not been applied to semiconductor device processes, due to a reduction in perpendicularity and a low resolution of a pattern when absorption increases.
To overcome the above-mentioned problems, the resin composition of the present invention has a high Tg and high etching resistance owing to an olefin monomer containing a cycloolefin in the main chain or an alicyclic group in the side chain. Also, etching resistance increases with the side chain generating from alicyclic group, which has acid-labile group to act as a high etching resistance.
The resin composition of the present invention comprises an olefin monomer containing cycloolefin in the main chain or an alicyclic group in the side chain or a polymer having a repeating unit of maleic acid derivatives or fumaric acid derivatives and a resist composition containing a polymer.
Now, the polymer and resist composition as such will be described in detail.
Polymer
A polymer to be used in the present invention is an olefin monomer, maleic acid derivatives or fumaric acid derivatives containing a cycloolefine in the main chain or an alicyclic group in the side chain as a repeating unit.
Alternatively, the polymer can be synthesized by adding acrylate, vinyl ether and styrene derivatives. The polymer to be synthesized in the present invention is insoluble or non-soluble in an alkaline solution in itself. However, it can also be soluble in the alkaline solution. Even if the polymer usually has an acid-labile group in the side chain, it may not have the acid-labile group all the time.
The solubility of the polymer to the alkaline solution depends on the content of the acid-labile group decomposed by acid. The solubility decreases with an increase in the content of the acid-labile. As a monomer type and its content in the polymer are varied, there may be a decrease or increase in solubility. Generally, as the number of hydrophobic groups increases, its solubility to the alkaline solution decreases. The substrate using the polymer obtained by controlling a repeating unit type and its content has good adhesion, non-dependency, sensitivity and resolution.
The polymer of the present invention is a multi-cyclic polymer represented by above-mentioned formula 1.
As shown in formula 1, a and b have to be adjacent each other and their content is preferably greater than 30% to the total monomer contents. If the content of a and b is less than 30%, developability to develop a solution after exposure decreases.
Preferably, the amount of alicyclic group in the main chain or side chain of the polymer should be at least 5%. If the amount of the alicyclic group is less than 5% in content, its etching resistance of the resist reduces.
The polymer represented by formula 1 is a resin containing more than 2 derivatives for each repeating unit of a, b, c, d, e and f in a monomer. For example, the monomer represented by repeating unit c in formula 1 contains its derivatives cxe2x80x2, cxe2x80x3 and cxe2x80x2xe2x80x3 as shown below in formula 2:
where a and b of the repeating unit are defined identical to those in formula 1, and cxe2x80x2+cxe2x80x3+cxe2x80x2xe2x80x3 is the same as c in formula 1.
The multi-cyclic copolymer includes block, random and graft copolymers.
Synthesis of the polymer represented by formula 1 can be made by a common method. Preferably, it may be made by radical polymerization. At this time, the radical polymerization can be initiated by some initiators, such as azo-bis isobutyronitrile(AIBN), benzoyl peroxide(BPO), lauryl peroxide, azobisisocapronitrile, azobisisoballeronitrile and t-butyl hydroperoxide.
Polymerization methods are available, for example, bulk polymerization, solution polymerization, suspension polymerization, bulk-suspension polymerization or emulsion polymerization. Polymerization solvent may be selected among benzene, toluene, xylene, halogenated benzene, diethylether, tetrahydrofurane(THF), ester class, ether class, lactone class, ketone class and amide class.
Another method to obtain the polymer represented by formula 1, maleic anhydride radically polymerized with at least one derivative selected among the cycloolefin derivative, olefin derivative, styrene deriviative, acrylate derivtive and vinyl ether derivative. After generation of a carboxylic acid group through hydrolysis or alcoholysis reaction, the group is esterificated totally or partially.
Polymerization temperature is controlled with a type of a catalyst and a molecular weight distribution of the polymer with various amounts of an initiator and reaction time. After completion of the reaction, it is preferable that those un-reacted monomer and side products remained in the reaction mixture should be eliminated by precipitation.
Average molecular weight (MW) of the polymer, as represented by formula 1, is measured by gel permeation chromatography(GPC) to be generally 2,000 to 1,000,000, preferably, 3,000 to 50,000 in consideration of sensitivity, developability, coatability and thermal stability as a photo-resist. The molecular weight distribution of the polymer may be 1.0 to 5.0, more preferably, 1.0 to 2.0.
Detailed reaction example of the polymer represented by formula 1 will be described below. However, the present invention should not be limited to the following examples.